In recent medical field, electronic endoscopes are frequently used for diagnoses and treatments. The electronic endoscope has a probing portion that is inserted into a body cavity of a subject under inspection, and an imaging unit including a CCD or the like is incorporated in a distal end of the probing portion. The electronic endoscope is also connected to a light source unit, so that light from the light source unit is projected from the distal end of the probing portion to illuminate the inside of the body cavity. While the inside of the body cavity is being illuminated, subject tissues inside the body cavity are imaged by the imaging unit. Captured images are processed in various ways in a processor which is also connected to the electronic endoscope, and the processed images are displayed on a monitor.
The electronic endoscope thus visualizes the inside of the body cavity of the subject under inspection in real time fashion. The captured images of the interior of the body cavity not only show the whole subject tissues but also individual details of the subject tissues, including fine or capillary vessels, deep blood vessels, pit patterns or gland orifice structures, as well as tissue surface asperities like concavity and convexity. Observing the condition of the subject tissues as the whole and in detail allows making diagnoses as to whether there are any lesions like a tumor.
When the operator of the endoscope detects a lesion from the image of the body cavity, the operator will usually scan the periphery around the detected lesion to search for metastasis of this lesion. For this purpose, the operator moves the distal end of the probing portion up and down or turns the direction of the distal end inside the cavity. However, it sometimes happens that the endoscope loses trace of the initially-detected lesion after the metastatic search in the peripheral area. To prevent this, JPA 2002-095625 suggests detecting a lesion as feature points from endoscopic images and tracing the feature points so as not to lose sight of the lesion.
In the prior art disclosed in JPA 2002-095625, patterns of the feature points of the lesion may be recognized to trace the lesion based on the recognized patterns. However, exact and steady detection of a similar portion to the recognized patterns from newly captured images can be difficult. Accordingly, the target tracing method based on pattern recognition can be less accurate.
The present invention has an object to provide an electronic endoscope system, a processor for an electronic endoscope and a target tracing method, which make it possible to trace a target such as a lesion accurately and steadily even while a doctor or operator is zooming an endoscopic image or moving the distal end of the endoscope in various directions during the imaging.